Relations of moderate and vigorous physical activity to fitness and fatness in adolescents

Background: It is unclear how moderate and vigorous intensities of physical activity (PA) are associated with cardiovascular fitness (CVF) and percentage of body fat (%BF) in adolescents. Objective: We tested the hypothesis that vigorous PA, to a greater degree than moderate PA, would be associated with better CVF and lower %BF. Design: This was a cross-sectional study of 421 black and white high school students ((x) over bar age: 16 y). PA was measured with 5 d of accelerometry and expressed in min/d of moderate or vigorous PA. CVF was measured with a multistage treadmill test and was expressed as the oxygen consumption at a heart rate of 170 bpm. %BF was measured with dual-energy X-ray absorptiometry. Multiple regressions were used to determine the degree to which variance in CVF and %BF was explained by PA, after control for age, sex, race, and the sex X race interaction. Results: A higher index for CVF was associated with higher amounts of moderate and vigorous PA; more variance was explained by vigorous than by moderate PA. Lower %BF was associated with higher amounts of vigorous PA but not with the amount of moderate PA. Conclusion: Black and white adolescents who engaged in relatively large amounts of free-living vigorous exercise were likely to be relatively fit and lean.